Thermostatic switch



Sept. 17, 1929. 1, THOMAS 1,728,811

THERMOSTATI C SWITCH Filed Aug. 6, 1927 INVENTOR fry/h 63 Thomas.

, ATCI'ORNEY Patented Sept. 17, 1929 UNITED STATES PATENT OFFICE mviNGREY THOMAS, or MANSFIELD, 0111c, ASSIGNOR TO WESTINGHOUSE ELECTRIC &MANUFACTURING COMPANY, A CORPORATION or PENNSYLVANIA THEBMOSTATIC SWITCHApplication filed August 6, 1927. Serial No. 211,054.

My invention relates to temperature-control devices and particularly tothermostatic switches of the quick-make-a-nd-break type.

An object of my invention is to provide a thermostatic switch that shallbe simple in construction, compact, rugged and easily manfactured.

Another object of my invention is to pro-- vide a radiant heater for asnap-acting thermostatic member ofa thermostatic switch that shall be ofsimple construction and easily applied to the switch.

.And a further object of my invention 15 to provide a heater for asnap-acting thermostatic member that shall have a relatively smallthermal capacity, and a relatively high radiant-heat capacity, in orderthat the disc may be caused to respond quickly to changes inenergization of the heater. I

For a fuller understanding of my invention, reference may be had to thefollowing description taken in conjunction with the accompanyingdrawings, in which:

Figure 1 is a top plan view of a switch-base structure embodied in myinvention.

Fig. 2 is a view, partially in section, of an assembled thermostaticswitch embodying my invention, and

Fig. 3 is a view of a radiant-heat-producing element for the-deviceillustrated in Figs. 1 and 2.

In Fig. 1 of the drawings is illustrated a base 11 having washers 12 and13 of insulating material mounted thereon, the washers being providedwith openings at substantially the central portions thereof. In orderthat the washers may beheld in a relatively fixed position with respectto each other, an eyelet 14 is provided that clamps the two washerstogether. As shown, the washer 13 is of a smaller diameter than thewasher 12 for a purpose to be hereinafter set forth.

A plurality of contacts 15 to 18, inclusive, and 19 are disposedcircumferentially in spaced relation about the washer 13 and located onthe washer 12 so as to be insulated from the base 11. The contacts beingof arcuate-shape and located against the edge of the washer 13, turningor disarrangement of the contacts is prevented. The contacts 15, 16

and 19 are secured to the base 11 by means of rivets 21 that extendthrough the base 11 and the contact members, the ends of the rivetsbelng peened over at 22. The rivets 21 may be lnsulated from the base 11by washers 23 of suitable insulating material.

The contact members 17 and 18 may be secured to the base 11 by rivetportions 24 and 25 of terminals 26 and 27, respectively, the ends of therivets being peened over at 28 on to the contacts 17 and 18 in order tohold them securely in place. The terminals 26 and 27 may be insulatedfrom the base 11 by washers 29 of suitable insulating material.

In order that an electric circuit may be completed between the terminals26 and 27, adjacent ends 31 of the contact members 16 and 17, 18 and 19,19 and 15.are engaged by contact-bridging members or buttons 32 that arecarried by a thermostatic bimetallic disc 33, the buttons beinginsulated from the disc by washers 34 of insulating material. The disc33 is supported on the base by means of a stud-bolt 36 that hasscrew-thread engagc ment with the base 11 at 37, and cooperating nuts 38between which the disc is.positioned. The pressure existing between thecontact buttons 34 and the contacts 15 to 18, inclusive, and 19 may beadjusted, by means of the stud-bolt 36, to any desired value, afterwhich the bolt may be held in the desired position by a lock washer 41and a nut 42.

The thermostatic disc 33 is of the type disclosed in U. S. Patent1,448,240 to J. A. Spencer. The disc there disclosed has thecharacteristic that, when heated to a temperature of a redeterminedvalue, the curvature of the iso is in one direction and, when cooled toa temperature of a predetermined value, the curvature is caused toreverse in direction. Thus, the disc has two opposed limiting positionscorresponding to two temperatures of predetermined values, thedifference between which may be determined by the heat treatment andmanufacturing processes applied to the disc.

Ordinarily, the difference between these temperatures is quite large,which difference may be designated the temperature differential of thedisc. In some instances, for examof the contact buttons 33 from thecontact members 15 to 18, illClllSiX'Q, and 19. In order to effectrcengagement of the contact members, the disc must be cooled to atemperature of say 400 F., in which case, the telnperature differentialof the disc will be substantially 100 F.

If a thermostatic switch embodying the disc S3having a temperaturedifferential of 100 F. is utilized for controlling a heating element inaccordance with the temperature of a heated device; for example, thefiat iron, the temperature at the ironing surface thereof will varybetween substantially two temperatures, the difference between whichwould be substantially 100 F. or more. In order that the temperature atthe ironing surface of the flat iron may vary between say 400 F. and450, the disc 33 must be caused to engage and be disengaged from thecontact members thereof with greater rapidity. To accomplish thisresult, an auxiliary heating element 44 is provided.

The heating element 44 comprises a relatively short conductor ofsuitable resistance material, the terminals of which may be spotweldedeither to the rivets 21 or to the concontacts 15 and 16 in circuit withthe terminals 26 and 27. In order that the conductor or resistanceelement 44 may not warp or bend to touch the disc 33, an eyelet 45 isprovided in the washer 13 that loops over the heating element, therebyholding it in place.

The heating element 44 heats the disc 34 by radiant energy and causesthe disc to respond quickly to current traversing the switch. Since theelement is of small mass, it will cool quickly, when disengagement iseffected between the contact members of the switch, and cause the discto return to its circuit-making position or the position shown in Fig. 2of the drawings.

The heat-generating capacity of the element 44 need not be sufficient tocause the disc to be actuated to its open-circuit position, in theabsence of other sources of heat, but, if the switch illustrated in thedrawings is utilized for controlling the temperature of a flat iron, forexample, the heat-generating capacity of the element 44 may besuflicient to heat the disc 34 to the temperature of 500 F. when thetemperature at the ironing surface of the fiat iron has reached a valueof say 450 F. Since the heating element 44 has relatively small thermalcapacity, the disc will cool quickly and will again cause the switch toreturn to its circuit-closing position when the temperature at theironing surface of the flat iron has fallen to approximately 400 F.

The heating element 44 being located between the disc 33 and the base 11in close proximity thereto, only a small amount of electric energy isrequired to increase the temperature of the disc to the value desired.The heating element is inexpensive, easily applied to the switch ande'liicient in its operation.

Various modifications may be made in the configuration and the structureof the device embodying my invention without departing from the spiritand scope thereof. I desire, therefore, that only such limitations shallbe placed thereon as are imposed by the prior art and the appendedclaims.

I claim as my invention:

1. A thermostatic switch comprising a base, spaced contact memberscarried thereby, a snap-acting thermostatic member secured to the base,contact members carried by the thermostatic member for bridging adjaccnt ends of said contact members and radiant heating means secured tocertain of said contact D1OI11- bers in electric circuit therewith forheating said thermostatic member.

2. The combination with a switch base, spaced contact members mountedthereon, a snap-acting thermostatic disc, contact members carried bysaid disc for engaging said spaced contact members, and means forsupporting the disc from said base, of heating means disposed betweensaid base and disc for heating said disc by radiant heat, and means forsecuring heating means to said spaced contact members and for connectingthe heating means in circuit therewith.

3. A thermostatic switch comprising a base, contact members mounted onsaid base, a snap-acting thermostatic disc on said base for cooperationwith said contact members and a radiant heat-producing element connectedto said contacts and mounted between said base and said disc.

4. A thermostatic switch comprising a base, contact members mounted onsaid base, a snap-acting thermostatic disc on said base for cooperationwith said contact members and a radiant heat-producing element connectedto, and supported by, said contact members for heating said thermostaticdisc.

In testimony whereof, I have hereunto subscribed my name this first dayof August,

IRVIN GREY- THOMAS.

